Understanding The Seafloor. Dr. Frank R. Hall. Resources for pictures, etc. used in this presentation

Transcription

1 Slide 1 Understanding The Seafloor Dr. Frank R. Hall Geological Oceanographer University of New Orleans New Orleans, LA 2003 This is a presentation prepared in the Summer 2003 for the Gulf Coast COSSEE by Dr. Frank R. Hall Slide 2 Resources for pictures, etc. used in this presentation US Geological Survey John s Hopkins University University of Wyoming NASA National Center for Atmospheric research Kohler, Inc. BayofFundy.com University of North Carolina NOAA American Museum of Natural History University of North Dakota PlateTectonics.com VIMS World Book Encyclopedia amonline.net.au Columbia University EPA Bowling Green State University Slide 3 I d like to thank Dr. Robert Pockalny University of Rhode Island for Use of His Video of a Mid Ocean Ridge

2 Slide 4 The Earth s Interior Slide 5 Three Rock Types on Earth s Crust Granite Basalt Gabbro Slide 6 Where does the seafloor begin? We have a terrestrial bias Earth s surface is > 70% water > 97% of this water is seawater

3 Slide 7 Land-Sea Morphology From the World Book Encyclopedia Slide 8 The Seafloor is a Basin Bathtub by Kohler

4 Slide 9 Water Facts Slide 10 Map of the Seafloor

5 Slide 11 Passive Margins An example of the structure of passive continental margins. Notice the delta lobe at the bottom. These are called Deep-sea fans. Slide 12 Passive Margin Profile Littoral Zone Neritic Zone

6 Slide 13 Continental Shelf Littoral (0-20m) Neritic (20-500m) Slide 14 Littoral Zone Shallowest, Tidally Influenced Where the Oceans meet the Land Marshes Estuaries Beaches, Bars, Barrier Islands, Cheniers Coral Reefs Deltas Slide 15 Hurricane Lili: 2002 Severe storms impact the Littoral zone

7 Slide 16 Marshes Habitats for many forms of life Typically quiet in terms of currents Sediments are typically fine-grained (muds) Slide 17 Estuaries The following four slides are from the University of North Carolina Semi-enclosed water bodies There are four kinds of estuaries Satellite Image of Delaware and Chesapeake Bays Slide 18 Salinity structure of an estuary Large riverine inputs: Fresh water floats on top of salt 1) Highly stratified estuary (Salt-Wedge) Sea water (more dense) Freshwater inflow (less dense) E.G., Chesapeake Bay

8 Slide 19 Salinity structure of an estuary 2) Partially mixed Tides mix salt water into fresh E.G., San Francisco Bay Slide 20 Salinity structure of an estuary Low riverine inputs, large tidal influence mixes waters 3) Well mixed E.G., Narragansett Bay Slide 21 Salinity structure of an estuary 4) Fjord-type estuaries Only found where glaciers have influenced the coast. E.G., Inderbitzen Fjord (Canada)

9 Slide 22 Beaches, Bars, Barrier Islands, Cheniers Slide 23 Deltas

10 Slide 24 Neritic Zone On most passive margins, neritic zones are basically inactive. That is to say, sediments are typically not being delivered to this part of the shelf by rivers. A notable exception is the Shelf off Brasil where the Amazon River brings sediemnts up to the shelf break. Slide 25 Continental Slope The Hudson Canyon is an example of an incised feature on continental slopes. Passive margins, canyons are typically inactive

11 Slide 26 Continental Rise Deep-Sea Fans USGS Image of the Mississippi River fan Slide 27 The Abyss Nares Abyssal Plain Abyssal Plain Islands Abyssal Hills Abyssal Hills exist under the abyssal plain: the sediment cover results in a smooth seafloor.

12 Slide 28 (Mid) Ocean Ridges aka Spreading Centers The longest, continuous feature on the Earth s Crust. A volcanic mountain chain that stretches around the world In the Atlantic and Indian Oceans, the Ridge is indeed in the Middle. Hoewever, in the pacific, it is on the eastern side of the basin. Thus, it is called the East pacific Rise. Breakes along the path of the ridge are called Fracture Zones or Transform Faults. Slide 29 Spreading Centers and Plate Tectonics At spreading centers, new seafloor is crated as hot, molten rock rises through the volcanoes. This is the upward movement of convection cells within the mantle.

13 Slide 30 The Graben of the East Pacific Rise Video taken from the Alvin on the East Pacific Rise in 1994 A graben is a depression. In this case, it denotes the axial valley associated with the east pacific Rise. (From Dr. Robert Pockalny, University of Rhode Island) Slide 31 Heat Flow and Plate Tectonics As you move way from the spreading center, you move into older oceanic crust older seafloor As the seafloor ages, it slowly cools, increases in density, and sinks to deeper depths. Slide 32 Spreading Centers: Evidence of Plate Tectonics Magnetic Stripes that Parallel the Ridge

14 Slide 33 Trenches: Subduction Zones At subduction zones, older ocean floor, that began at the spreading centers, dive into the mantle. Earthquakes are very common in areas of subduction. The seafloor around Australia has the Philippine Plate colliding with the Pacific Plate that dives underneath forming a trench. Slide 34 Hot Spots The Formation of Hawai i Your homework assignment relates to this phenomenon. Are hotspots permanent features on the Earth?

15 Slide 35 Deep-Sea Sediments Four Sources Terrigenous (derived from land) Biogenic (remains of organisms) Chemical (usually as precipitates) Extraterrestrial (micrometeorites and tektites) Slide 36 Terrigenous Rivers Wind Glaciers Icebergs

16 Slide 37 Terrigenous Volcanic Eruption: Mt. Pinatubo Slide 38 Biogenic Calcareous Siliceous Chitonous Phosphatic Phosphatic includes things like fish scales and bones. In addition to calcareous foraminifera, there are also agglutenated varieties that make their shells out of surrounding sediment.

17 Slide 39 Chemical Black Smoker from a Hydrothermal Vent Slide 40 Extraterrestrial Meteorites impact the Earth from outer space. Meteorite Tektite Although grouped with extraterrestrial objects, tektites are actually created from Earth materials that are ejected into the air when a meteorite hits. Slide 41 Homework Assignment HOTSPOTS are thought of as fixed features on the Earth s surface, but are they really? This will be your homework assignment: Examine and report on new data that suggests that the Hawaiian Hotspot moved over time. Prepare a 3-5 page (1 inch margins, 1.5 linespace, 12 pt Times New Roman font) report on Hotspots and the implications of the Hawaiian Hotspot moving. Examine the results of Ocean Drilling Leg 197: